How fast does lava run down the mountain when the volcano erupts?

Answers

It depends, for there are several types of volcanic eruptions, each of which produces a different effect on the lava coming out. Plinian eruptions are the most explosive and have the fastest burst of lava coming out. These eruptions also produce a large amount of pyroclastic flows. The lava itself coming down a mountain is not as fast as the pyroclastic flows, which is comprised of “fluidized masses of rock fragments and gases that move rapidly in response to gravity.” Large pyroclastic flows can move as fast as 200 meters per second. For more information about the different kinds of eruptions click the first link below. For more information on pyroclastic flows, visit the second link provided below.

The composition of the lave that erupts has an effect on how fast it flows. If lava is viscous it means that it is thick with the consistency of syrup. This lava flows slowly though it also can move far distances. If lava has low viscosity, it flows quickly. This is true of basaltic lava. Even the fastest lava flow, however, still only travels at a few kilometers per hour and can be easily outrun.

Another factor of lava flow is how much water it joins with on its way down. Volcanic mountains that have snow often form rivers of mud and lava called lahars as the heat from the volcano eruption melts the snow. This can form a floodlike flow that is very fast, dangerous and far-reaching.